1. Field of the Invention
The present invention relates to a shift control device for an automatic transmission. More specifically, the present invention relates to techniques for improving the shift quality by the so-called shift elements wherein an interference shift element such as a dog clutch is switched from an engaged state to a disengaged state while a friction shift element such as a friction clutch or a friction brake is switched from a released state to a locked state.
2. Background Information
For example, one of the existing automatic transmissions proposed is the automatic transmission described in Japanese Unexamined Patent Publication No. 2010-188795, which is an automatic transmission that shifts gears by switching the interference shift element such as a dog clutch from the engaged state to the disengaged state, and by switching the friction shift element such as a friction clutch or a friction brake from the released state to the locked state.
The automatic transmission system used in the motor transmission system for a hybrid vehicle selects and uses either a high speed transmission system that transmits the rotations of the electric motor at high speed, or a low speed transmission system that transmits the rotations of the electric motor at low speed. In short, placing the dog clutch in the engaged state and the friction clutch in the released state thereby allows selection of the low speed transmission system, and placing the dog clutch in the disengaged state and the friction clutch in the locked state allows selection of the high speed transmission system.
In the case of this kind of automatic transmission, when switching (shifting) from the state of using the low speed transmission system to the state of using the high speed transmission system, the shifting (upshift) involves switching the dog clutch from the engaged state to the disengaged state, and switching the friction clutch from the released state to the locked state.
In the automatic transmission described in Japanese Unexamined Patent Publication No. 2010-188795, when shifting, the shifting (upshift) is performed by first, switching the dog clutch from the engaged state to the disengaged state, and thereafter switching the friction clutch from the released state to the locked state.